Biological Systems

a. Bionanotechnology

Micro/nano-scale biotools for cell transfection and analysis are being developed to achieve cell-specific experimental capabilities and localized cell-tool interfaces. This allows for minimal perturbation to cells and unprecedented spatial resolution, which is essential for fundamental cell studies.

The ability to precisely deliver molecules into single cells is of great interest to biotechnology researchers for advancing applications in therapeutics, diagnostics, and drug delivery toward the promise of personalized medicine. The use of bulk electroporation techniques for cell transfection has increased significantly in the last decade, but the technique is nonspecific and requires high voltage, resulting in variable efficiency and low cell viability. In Prof. Espinosa's lab, I have developed a new tool for electroporation using nanofountain probe (NFP) technology that can deliver molecules into cells in a manner that is highly efficient and gentler to cells than bulk electroporation or microinjection.

To trigger formation of nanopores on the cell membrane by electroporation, a transmembrane electric potential in the range of 0.2~1 V is required. An accurate prediction of this local field is essential to determine the critical applied voltage for nanopore formation and optimal probe location with respect to the cell membrane. Unlike bulk electroporation where each individual cell is exposed to a uniform electric field, the electric field for single cell electroporation is often non-uniform and hence an analytical solution is not feasible. Therefore, I used COMSOL Multiphysics to simulate the distribution of the electric potential through a cell membrane.

The multiphysics analysis of the mechanism of NFP-E reveals that application of the voltage creates a localized electric field between the NFP cantilever tip and the region of the cell membrane in contact with the tip. Therefore, NFP-E can deliver molecules to a target cell with minimal effect of the electric potential on the cell. In addition, the model predicted that the onset of cell-NFP contact can be accurately monitored by measuring the electrical resistance between the NFP tip and cell, which would increase suddenly with a gap size between NPF tip and cell of <50nm. This predicted detection method for cell-NFP contact was experimentally confirmed as we observe a sudden increase, up to 143%, in the resistance. Further experimental studies confirm that NFP-E offers single cell selectivity, high transfection efficiency (>95%), dosage control, and very high viability (92%) of transfected cells.

Publications (IF: 5-year Impact Factor)

W. Kang, R. McNaughton, and H. Espinosa, In Vitro Micro- and Nano-scale Technologies for Delivery into Adherent Cells, 34 (8), 665–678, Trends in Biotechnology, 2016 (Highlighted in BRIC.org, IF: 12.1).
S. Nathamgari, B. Dong, F. Zhou, W. Kang, J. Giraldo-Vela, T. McGuire, R. McNaughton, C. Sun, J. Kessler, H. Espinosa, Isolating Single Cells in a Neurosphere Assay Using Inertial Microfluidics, 15 (24), 4591-4597, Lab on a Chip, 2015 (Highlighted in ScienceDaily, Nanowerk, Biology News Net, etc, IF: 5.8).
J. Giraldo-Vela, W. Kang, R. McNaughton, A. Chen, A. Tsourkas, and H. Espinosa, Single Cell Detection of mRNA Expression Using Nanofountain Probe Electroporated Molecular Beacons, 11(20), 2386-2391, Small, 2015 (Featured as the cover article, IF: 8.4).
W. Kang, J. Giraldo-Vela, S. Nathamgari, T. McGuire, R. McNaughton, J. Kessler, and H. Espinosa, Transfection of Postmitotic Neurons Using a Microfluidic Localized Electroporation Device, 14(23), 4486-4495, Lab on a Chip, 2014 (Featured as the inside back cover; Highlighted in ScienceDaily, EurekAlert, Phys.Org, etc, IF: 5.8).
W. Kang, R. McNaughton, F. Yavari, M. Minary-Jolandan, A. Safi, and H. Espinosa, Microfluidic Parallel Patterning and Cellular Delivery of Molecules with a Nanofountain Probe, 19(1), 100-109, Journal of Laboratory Automation, 2014.
W. Kang, F. Yavari, M. Minary-Jolandan, J. Giraldo-Vela, A. Safi, R. McNaughton, V. Parpoil, H. Espinosa, Nanofountain Probe Electroporation of Single Cells, 13(6), 2448-2457, Nano Letters, 2013. (Highlighted in ScienceDaily, Bio-Medicine, Technology Network, FierceDrugDelivery, National Institute of General Medical Sciences, etc, IF: 14.9)
Safi, W. Kang, D. Czapleski, N. Moldovan, and H. Espinosa, Optimized Nanofountain Probes Geometry and Microfabrication Throughput for Large-Scale Nanopatterning, 23(12), 125014, Journal of Micromechanics and Microengineering, 2013.

b. Biomechanics

Accurate characterization of cavitation properties in soft gels and fundamental understanding of the complex cavitation-gel coupling are essential to establish the reliable bounds of

the critical mechanical inputs (acceleration or pressure) that will likely induce cavitation in biological samples. Toward clinically and biologically relevant studies of cavitation, it is still necessary to develop a reasonable in vitro model that biologically and mechanically represents target organs. As an example, neurons can be cultured in 3-dimentional extracellular matrix (ECM) at a specific concentration to match mechanical stiffness of the neuron-ECM system to target brain tissues. Biological studies utilizing such neuron-ECM system would provide heterogeneous cavitation nucleation criteria in brain and shed light on key mechanism(s) in traumatic brain injury.

Publications (*: corresponding author)

W. Kang*, A. Adnan, T. O'Shaughnessy, and A. Bagchi, Cavitation Nucleation in Soft Materials: Experiment and Mechanism, DOI: 10.1016/j.actbio.2017.11.030, Acta Biomaterialia, 2017 (IF: 6.8).

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